1. Field of the Invention
The present invention relates to the enhanced recovery of crude oil from zones or formations within a well. More particularly, the present invention the relates to the use of acoustic energy to enhance water injection techniques. Additionally, the present invention relates to the production of acoustic signals through the force of a fluid flowing through the injector tubing.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The production of crude oil from a formation is initially supported by the expansion of fluids in the pore system and then, as the reservoir pressure falls below the bubble point of the oil, the expansion of solution gas provides pressure support. This phase of the reservoir life is called primary recovery. Some reservoirs are connected to an aquifer and the flow of water from the aquifer provides pressure support to displace the crude oil to the producing wells.
As the production rate of crude oil declines under primary recovery mechanisms, secondary oil recovery techniques are used to provide pressure support for the oil reservoir. The most popular technique is water injection into the oil zone and is called water flooding. For high viscous oils, steam flooding is used to provide pressure support, reduce the thermal viscosity and increase the mobility of the oil. For lighter oils, gas injection can be used to induce gravity drainage of the oil toward the structurally lower production wells and this method is called gas assisted gravity drainage; however, if steam is the injected gas, it is called steam assisted gravity drainage.
In order to improve the ability to recover oil above that normally possible with secondary recovery techniques, tertiary oil recovery techniques are used. A tertiary method commonly used in zones being water flooded includes the use of diversion agents such as polymers to increase water viscosity and plug off swept zones to improve vertical and horizontal sweep efficiencies. To mobilize residual oil in the areas already swept by water, surfactants and caustic agents are mixed with the injected water to reduce surface tension, but absorption of the expensive surfactants on clay particles limits the application to cleaner formations. This type of flood is called an alkaline, surfactant and polymer flood (ASP flood).
An experimental tertiary oil recovery technique is the use of low frequency acoustic energy to increase oil recovery in water floods and natural water drive oil reservoirs. Seismic sources (6-40 Hz) have been pilot tested on shallow oil zones in Russia with documented success on high water cut wells where the oil cut increased from 1-2% to 8-12% while the water production rate remained constant. This increased oil cut returned to normal over a one to four week period following termination of the seismic stimulation.
U.S. Pat. No. 2,700,422 by Bodine describes using seismic (1 to 30 Hz) vibration to stimulate the oil producing formation. A standing wave in a fluid or metal bar is used to stimulate the formation with a surface source or a standing tube wave is used to stimulate the formation with a down hole source. The major shortcoming with this constant frequency acoustic stimulation method in natural sediments is that the sonic energy can reflect away from the oil formation or it can attenuate before reaching the oil formation. Field trials using various transmission forms of the method show little or no effect on oil production due to the acoustic energy not reaching the oil formation.
U.S. Pat. No. 6,015,010 extends the Bodine method by using a down hole pump to generate a very high pressure pulse or shock wave in the well bore. The shock wave produces a broad banded, low frequency (10 to 250 Hz) acoustic pulse. Field trials show the source frequency band can overlap a guided wave frequency in the oil formation and this single frequency can be measured more than 1000 ft away from the source. Field production tests using the source have shown a decrease in oil decline rate.
Sonic stimulation conducted for one hour to several days (1-3 kHz) in well bores of producing wells has shown a permanent increase in oil production over the life of the wells. This effect is attributed to removal of skin damage in the near wellbore area by mobilizing clay fines, liquefying paraffin build up and emulsifying solid asphaltenes back into the liquid oil phase.
Ultrasonic treatment (16 to 30 kHz) of perforated intervals, gravel packs and slotted liners in producing wells has been used to remove carbonate and sulfate scale build up. The ultrasonic treatment process creates cavitations that fracture the scale into particles that are then produced to the surface along with the fluids. Ultrasound usually attenuates within several wellbore diameters from the casing or liner surface, thus the usefulness of ultrasonic stimulation is limited to the near well bore area.
Core tests with seismic frequencies (6-100 Hz) have shown improved or accelerated oil recovery by coalescing individual oil droplets into a continuous oil phase, reducing capillary force as a result of the core becoming more water wet, reducing interfacial tension between heavy oil and brine, and releasing solution gas from the liquid oil phase even though the average reservoir pressure is above the bubble point. The release of solution gas can cause the effect of seismic stimulation of the reservoir to last for weeks while the gas is being dissolved back into the oil phase.
U.S. Pat. No. 3,754,598 shows using low frequency (0.001 to 25 Hz) oscillatory pressure injection to increase the sweep efficiency of a pattern water flood or surfactant flood. The amplitude of the pressure pulse would range from 10 p.s.i. to fracture pressure of the reservoir. For synthetic cores with uniform permeability and porosity, oscillatory pressure injection can increase injectivity by a factor of 2.5 and decrease residual oil saturation by 10%. While core tests have shown positive oil recovery results for acoustic frequencies ranging from 30 Hz to 40 kHz, field pilot tests have shown mixed results. In pilot tests that have failed using surface seismic sources, hydrophone recordings showed that either the formation was too deep or there was a major reflection or absorption layer between the source and the target formation. In pilot tests that have failed using well bore acoustic sources, hydrophone recordings have shown that the source frequency output had attenuated 30 decibels in the offset producing wells.
Cross well bore tomography of oil formations shows that specific frequencies resonate in the reservoir without attenuation while the majority of other frequencies attenuate 30 decibels in an offset well. Earth noise usually starts around −40 decibels (based on zero at the acoustic tool source) for low frequencies and core tests reveal that acoustic vibrations should measure 20 decibels above noise in order to have an effect on residual oil saturation. Cross well bore tomography also shows that guided waves can be stopped or reflected out of zone by faults and that thin shale lenses can increase the attenuation.
It is an object of the present invention to provide a sonic oil recovery apparatus that enhances oil recovery in production zones.
It is another object of the present invention to provide a sonic oil recovery apparatus which reduces electrical power requirements due to an increase in injectivity.
It is another object of the present invention to provide a sonic oil recovery apparatus which reduces the pressure requirements of the introduced fluid into the well.
It is a further object of the present invention to provide a sonic oil recovery apparatus which increases the injectivity of the fluid into the well.
It is a further object of the present invention to provide a sonic oil recovery apparatus that reduces scale build up on the piping.
It is still a further object of the present invention to provide a sonic oil recovery apparatus in which water, or other fluid, can be injected at a higher rate and at lower pressures.
It is still a further object of the present invention to provide a sonic oil recovery apparatus which can be used on various types of formations.
It is a further object of the present invention to provide a sonic oil recovery apparatus that can transmit a resonate frequency band to a nearby producing well without excessive attenuation from faults, pinch-outs, or other significant rock matrix changes.
It is a further object of the present invention to provide a sonic oil recovery apparatus which enhances heavy oil production by fluidizing sand in worm holes and by reducing oil viscosity.
It is a further object of the present invention to provide a sonic oil recovery apparatus which enhances oil production from a carbon dioxide flood by increasing the gravity segregation rate.
It is a further object of the present invention to provide a sonic oil recovery apparatus which improves sweep of surfactant and polymer floods by enhancing fluid mixing in dead end pore spaces, increasing absolute permeability in low permeability zones and preventing polymer build up in the near wellbore area.
It is still a further object of the present invention to provide a sonic oil recovery apparatus which minimizes turbulence in the fluid flow.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.